New magnetic state in thin-film antiferromagnets and intrinsic exchange bias

摘要

We observe a new magnetic state, for which zero magnetization at zero applied field (remanent magnetization) cannot be reached isothermally. It happens because the origin (M(H=0)=0) is outside the major hysteresis loop. This unusual state is observed in thin films of (110)-FeF_2 (nominally an antiferromagnet) grown on MgF_2. The surface is responsible for the macroscopically broken time-reversal symmetry, uncompensated magnetization (UM) in a nominally compensated antiferromagnet, and, ultimately, for the new magnetic state. Using symmetry group arguments and results of ab-initio calculations, we argue that it is an equilibrium state.